A light scanning device of an electrophotographic image forming apparatus includes a transparent window for transmitting a laser beam, deflected by a polygon mirror, to the outside of the light scanning device. Dust that adheres to the transparent window blocks the laser beam, as a result of which image quality of an output image is reduced. In particular, for the light scanning device that exposes a photoconductor from therebelow in a gravitational direction, toner that has fallen from a developing device due to vibration generated when a cartridge (in which the developing device and the photoconductor are integrated to each other) is removed adheres to the transparent window.
Regarding this issue, PTL 1 describes an image forming apparatus that allows a slit, provided in a light scanning device and that is used for passing a laser beam therethrough, to be dustproof by moving the slit by a shutter moving mechanism. FIG. 8 in PTL 1 illustrates a structure that moves a shutter in a first direction by a motor and that moves the shutter in a second direction using an elastic force of a spring that is connected to an inner wall of an opening provided in the shutter and an upper cover of the light scanning device.